This invention relates to storage of binary data, and more particularly to the propagation of magnetic domains in acoustic surface waveguides.
The concept of using cylindrical magnetic domains in a sheet of magnetic material to store binary data for computer memories and to carry out logical operations is being vigorously pursued by many researchers. One of the problems associated with this concept is the necessary minipulation of these so-called magnetic bubbles. In particular, it is necessary to move the bubble about, from input port, to storage location, to readout port. In the present invention guided acoustic surface waves are used to augment field access magnetic bubble propagation. Several schemes have been suggested in the past to regulate the bubbles' positions, all of which involve the use of magnetic drive fields. These drive fields are supplied either by current flowing through a pattern of conductors or by one of the field access approaches. These field access approaches involve immersing the entire sheet in either a pulsating or rotating magnetic field that acts on the bubbles by means of carefully placed spots of magnetic material that concentrate the field. The disadvantage with conductor methods is that a great many accurately placed conductors whose dimensions are comparable to the size of the bubble must be interconnected with external-access circuits. On the other hand, the pulsing bias field access method requires oversize high-inductance coils which make high frequency operation difficult. Finally, the rotating in-plane field technique requires two orthogonal drive coils operating 90.degree. out of phase. The need for two coils presents severe packaging problems and virtually eliminates internal access after assembly.
In addition to the manipulation of the bubble's position, it is also necessary to perform other processing functions, such as read and write, etc. To read the information, it is necessary to electronically detect the bubbles. A new system utilizing surface waves is presented that overcomes the need for bubble stretching required by other detection methods. There are two popular methods which utilize the bubbles stray fields already in existence. In the first method a Hall-effect sensor is placed on top of the magnetic crystal and if a bubble passes by, the Hall signal will be changed. In the second method the stray field of a bubble causes a change in resistance of a Permalloy element. Since the stray fields of a bubble are relatively weak, these effects are understandably small. Thus, the use of these techniques requires bubble stretching and complicated electronics to amplify and discriminate the "zero" bit from the "one".